This invention relates to a gas turbine engine of the type which includes an inlet particle separator and, more particularly, to apparatus for measuring the temperature of the air entering the compressor of such engines.
Gas turbine engines are commonly fitted with an instrument to measure the temperature of the working fluid entering the engine compressor. This device is generally referred to as a T2 probe since the fluid temperature immediately upstream of the first moving compressor stage is designated T2. The probe provides a signal proportional to T2 which is transmitted electrically, mechanically, hydraulically, or by a combination of these methods from the probe to the engine control system. The engine control system uses this signal to adjust engine speed, fuel flow and/or compressor stator vane angle to correct the aero-thermal characteristics of the engine and ensure proper function and power output for transient ambient conditions. Although necessary on stationary (land) gas turbines, this measurement of T2 is of prime importance in flight propulsion applications where sudden changes in ambient temperature occur due to altitude changes and the penetration of clouds and weather fronts. Since such changes in ambient temperature are often rapid, the response rate of the T2 probe must be sufficiently fast to allow correction of the engine's aero-thermal function to negate the possibility of compressor stall or other engine malfunction.
T2 probes currently used in gas turbine engines may be classified by their location in the engine. Such prior art T2 probes have either been located directly in line with the engine inlet airstream or have been located in a position remote from the main engine inlet airstream. Prior art mainstream and remote T2 probes may be electrical, mechanical, gas filled, or liquid filled.
Existing mainstream T2 probes generally provide good response rates but suffer several disadvantages. Their location in the main engine airstream creates turbulence in the area surrounding the probe and consequently provides aerodynamic wakes to the engine compressor. A further disadvantage is that such probes are subject to ice buildup in certain operating conditions which can cause foreign object damage to the engine. Consequently, such probes often must be fitted with an anti-icing system.
While a non-anti-iced mainstream probe provides a relatively fast and accurate output, anti-iced mainstream probes have lower response rates and often generate reading errors when the anti-ice system is activated. Further, anti-ice systems for such probes are often complex. Many probe anti-ice systems require hot compressor air and a variety of aero-thermal devices which result in performance penalties to the engine. Alternatively, electrical heating with its associated cost and complexity has also been used to anti-ice such prior art mainstream probes. Further, a failure of any of these prior art probe anti-ice systems may result in ice ball buildup around the probe and foreign object damage to the engine from ice ingestion.
Because of these problems with mainstream probes, other prior art engines have used remotely located T2 probes. Prior art remote T2 probes are generally mounted in a feed duct which draws air from the engine inlet over the probe and dumps it back into the engine inlet. The pressure differential required to flow the duct air has generally been provided by an eductor energized by high pressure air bled from the engine compressor. The loss of this air from the engine cycle has resulted in degradation of engine power and specific fuel consumption. The magnitude of this loss is dependent on the airflow and velocity necessary to generate the required probe response rate. While such prior art remote probes do not suffer from the icing problems of mainstream probes, response rate and accuracy improvements are desired, particularly during operation of engine anti-icing equipment at which time such prior art probes have exhibited transient reading errors.